Easy-opening container and closure with radiation-weakened bond and method therefor

ABSTRACT

An easy-opening container and a closure and method therefor are provided. The closure is bonded to a base portion of the container by a bond that can be weakened by radiation, such as microwave radiation. The bond can be weakened after a retort process or other operation so that the bond and, hence, the container is strong enough to resist the forces associated with retort processing but easily opened by a consumer or other user. Either or both of the closure and the base portion can be formed of plastic, and the container can be hermetically sealed for containing food or for other uses.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention relates to an easy-opening closure for hermetic sealing of an open end of a retortable container and an easy-opening container that is hermetically sealed by such a closure.

2) Description of Related Art

A variety of closures are known for the hermetic sealing of a container, such as conventional tin-plated steel cans that are widely used for containing food products. Retortable containers are those that can withstand a pasteurization or retort process comprising heat and pressure for preserving the food contents of the container. During retort, the container can be subjected to temperatures above 212° F., e.g., up to 280° F., under pressures of 15 to 30 psi.

Easy-opening containers are those that can be opened without undue effort and without the use of a special tool such as a rotary can opener. In order for an easy-opening container to be retortable, the closure must be sufficiently strong to resist stresses that develop as a result of the retort heat and pressure but easily overcome during opening. One conventional easy-opening, retortable container includes a closure that is stronger in shear than tension. The closure is strong enough to withstand the shear force that develops during retort, while a relatively small tensile force is required to open the container. For example, U.S. Pat. No. 5,752,614, titled “Easy-Opening Closure for Hermetic Sealing a Retortable Container,” to Nelson describes an easy-opening closure that includes a metal end ring that can be seamed to an open end of a retortable container and defines a central opening that is covered by a membrane patch. The membrane patch is bonded to the end ring such that the bond is unaffected during retort processing but has a predetermined tensile force strength that is preferably less than 5 psi to allow peeling of the membrane patch from the end ring. Thus, the container can be retorted and subsequently easily opened.

Other easy open containers are formed partially or wholly of plastic. For example, a lid that includes a metallic foil can be adhered to a plastic container, which can be used for retort. Attempts have also been made to manufacture retortable containers exclusively of plastic. For example, a plastic membrane can be heat sealed to a plastic container. Alternatively, the plastic membrane can be heat sealed to a plastic end ring that is similar to the metal end ring described by Nelson, and the plastic end ring can be fusion bonded to the container by spin welding. A pull ring or tab can also be provided on the plastic membrane so that a user can peel the plastic membrane from the container, thereby breaking the bond between the plastic membrane and the container or plastic end ring. The bond can be difficult to form by heat sealing due to the poor thermal conductivity of the plastic. Further, the bond must be sufficiently strong to resist the stresses that are applied during manufacture, for example, heat and pressure that occur during retort. However, if the bond is too strong, a user may be unable to open the container.

Thus, there exists a need for an easy-opening closure for hermetically sealing an open end of a retortable container and an easy-opening container that is hermetically sealed by such a closure. The closure should be strong enough to withstand the stresses induced during retort, but easily removed by a user. Additionally, the closure should be compatible with closures formed of plastic, in which a bond between plastic members is to be overcome during opening of the container.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an easy-opening container and a closure with a bond that is weakened with radiation so the container sealed by the closure can be easily opened by a consumer. The bond, which can join a plastic closure and a plastic body portion, can be weakened after a retort process so that the container is strong enough to resist the forces produced by internal pressures and temperatures that are associated with retort processing.

According to one embodiment of the present invention, the container includes a base portion with a bottom and side that define an interior space and an opening thereto. A plastic membrane of sufficient size to cover the opening has an outer peripheral area attached to the base portion by a bond having a predetermined shear force strength sufficient to withstand forces created during retort processing of the container. The bond is configured to be radiation weakened to have a predetermined tensile force strength to allow easy-opening of the container by peeling the membrane from the base portion. The base portion can also be formed of plastic and can include a plastic end ring that is fusion bonded to a body member such as the side of the container. The end ring can define the opening, such that the plastic membrane can be attached to the end ring by the bond to seal the container. The membrane and the base portion can be formed of a high barrier material, such as a co-extruded sheet of polypropylene and ethylene vinyl alcohol, to prevent transmission of moisture and oxygen therethrough. Oxygen scavengers can also be disposed in either the membrane or the base portion.

The bond can be formed of an adhesive such as polyurethane, and can be adapted to be weakened by radiation such as microwave radiation. For example, the shear force strength of the bond before weakening can be at least about 20 psi, the tensile force strength of the bond after weakening can be less than about 14 pounds.

The present invention also provides a method of hermetically sealing an open end of a retortable, easy-opening container. A plastic base portion defining an opening is provided, for example, by fusion welding an end ring to a body member. A plastic membrane is disposed to cover the opening of the base portion. The plastic membrane can be formed by co-extruding a sheet of polypropylene and ethylene vinyl alcohol. In addition, oxygen scavengers can be disposed in the plastic membrane. A bond is formed between the membrane and the base portion, for example, by disposing an adhesive between the plastic membrane and the base portion and urging the plastic membrane and the base portion together. The bond is irradiated with microwave or other radiation, and thereby weakened so that the bond allows easy opening of the container by peeling the membrane from the base portion. According to one aspect of the invention, the bond is formed with a shear force strength of at least about 20 psi and weakened to have a tensile force strength of less than about 14 pounds. Thus, the container can be retorted or otherwise processed after the bond is formed and before the bond is weakened.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a section view illustrating an easy-opening, retortable container according to one embodiment of the present invention configured for radiation weakening;

FIG. 2 is a perspective view illustrating the container of FIG. 1, with the closure shown partially removed from the base portion of the container; and

FIG. 3 is a block diagram illustrating the operations for hermetically sealing a retortable, easy-opening container according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

Referring now to FIG. 1, there is shown an easy-opening, retortable container 10 according to one embodiment of the present invention. The container 10 has a base portion 12, which defines an openable first end 16 that is closed by a closure 30, e.g., a peelable or otherwise removable membrane. Preferably, the base portion 12 is formed of one or more polymers. In the illustrated embodiment, the base portion 12 includes a body member and, in particular, a continuous cylindrical side 14 that extends longitudinally from the openable first end 16 to a second end 18, which is closed by a bottom 20. The side 14 can alternatively comprise other configurations, for example, multiple rectangular panels configured at right angles so that the base portion 12 has a square cross section instead of circular as shown. The bottom 20 can be formed separately from the side 14 and joined thereto, for example, by crimping, welding, gluing, and the like. Alternatively, the side 14 and the bottom 20 can be formed as a unitary member as shown in FIG. 1, for example, by thermoforming a multilayer high-barrier sheet, or by co-extrusion blow molding the side 14 and bottom 20 of plastic. Additionally, the side 14 can have a tapered shape, such as a conical shape, that includes the bottom 20.

The openable first end 16 is closed by the closure 30 such that the base portion 12 and the closure 30 define an interior space 22 therein, which can be hermetically sealed. As shown in FIG. 1, the base portion 12 can include an end ring 24 that extends circumferentially and radially inward from the side 14 to define an opening 26, which is smaller than the diameter of the side 14 at the first end 16. An outer peripheral area 25 of the end ring 24 can be fusion bonded to the side 14, e.g., by spin friction welding the end ring 24 thereto. Alternatively, the end ring 24 can be ultrasonically bonded or otherwise adhered or joined to the side 14. According to other embodiments of the present invention, the closure 30 is connected directly to the side 14 of the base portion 12 without the use of the end ring 24. Further, the base portion 12 can be formed by joining the closure 30 to a body member other than the side 14, i.e., a body member that defines other types or configurations of containers.

The closure 30 can be a generally planar membrane that covers the opening 16 of the base portion 12, e.g., an outer peripheral area 31 can cover an intermediate area 27 of the end ring 24 as shown in FIG. 1. The closure 30 can be a single layer structure or a multilayer structure. For example, the closure 30 can be formed by coextruding multiple layers to form a multilayer sheet and then cutting the sheet to the desired size and shape of the closure 30 with a die or other tool. Further, the closure 30 can be formed of the same or dissimilar materials as the base portion 12.

Preferably, both the base portion 12 and the closure 30 are formed of a high barrier material to prevent transmission of moisture, oxygen, and other fluids therethrough, such as where the container 10 is used in food packaging. Either or both of the base portion 12 and the closure 30 can include various types of plastic including, but not limited to, polyolefins such as polypropylene. For example, the base portion 12 and/or the closure 30 can be formed of multilayer structures that include layers of polypropylene, ethylene vinyl alcohol (EVOH), polyethylene, or the like. In particular, a multilayer structure can be formed by co-extruding polypropylene with ethylene vinyl alcohol. The material of the base portion 12 and closure 30 can also include chemical compounds that absorb oxygen, referred to generally as oxygen scavengers, to prevent the transmission of oxygen. For example, a moisture-activated, iron oxide-based oxygen scavenger can be disposed in polyolefin.

A bond 32 connects the closure 30 to the base portion 12, e.g., extending circumferentially around the opening 26 and connecting the closure 30 to the end ring 24. Preferably, the bond 32 is sufficiently strong to maintain the attachment of the closure 30 to the base portion 12 throughout the manufacture, filling, processing, and/or handling of the container 10, but configured so that the closure 30 can be removed from the container 10 by the user. For example, the bond 32 can be formed with a shear force strength of at least about 20 psi so that the container 10 can withstand a retort process in which the sealed container 10 is subjected to relatively high temperatures and corresponding internal pressure, or other processing operations. Subsequently, the strength of the bond 32 can be reduced, for example, to have a tensile force strength of less than about 14 pounds so that a user can open the closure 30 by lifting or peeling the closure 30 from the container 10. According to one embodiment of the present invention, the bond 32 is weakened to have a tensile force strength of between about 6 and 14 pounds so that the user can open the closure 30 by applying a force of no more than about 6 to 14 pounds. In other embodiments, the strength of the bond 32 can be further reduced.

The bond 32 can be formed of an adhesive, such as a polyurethane adhesive or nylon adhesive that is disposed between the closure 30 and the base portion 12. Polyurethane adhesives can be solvent-based or solvent-less. For example, polyurethane adhesives are available from Liofol Company, a division of Henkel Adhesives, Cary, N.C., including solvent-based and solvent-less polyurethane adhesives identified by product numbers 3649/6255 and 7975/7276, respectively.

The closure 30 can be formed separately from the base portion 12 and subsequently attached to the base portion 12. Various methods can be used for disposing the adhesive between the closure 30 and the base portion 12. For example, the closure 30 and/or the base portion 12 can be treated with a corona, which provides an electrostatic charge that forms a primed or roughened surface on which the adhesive can more easily be deposited uniformly. The adhesive is then applied to one or both of the closure 30 and the base portion 12, and the closure 30 is positioned and urged against the base portion 12.

As initially formed, the bond 32 is typically strong enough to withstand retort and other processing, but has a tensile force strength that requires more than the desired 6 to 14 pounds of lifting or peeling by the user. Therefore, the bond 32 can be subjected to radiation for weakening the bond 32. As shown in FIG. 1, a radiation source 40 can be used to emit radiation directed toward the bond 32, e.g., through the closure 30 as shown in FIG. 1. According to one embodiment, the radiation source 40 is connected to an electrical power source 42 and configured to generate microwave radiation that is directed toward the bond 32, e.g., electromagnetic radiation characterized by a frequency between about 300 MHz and 300 GHz. The bond 32 can be exposed to radiation for various durations, e.g., according to the material, size, and thickness of the closure 30, base portion 12, and bond 32; the frequency and amplitude of the radiation; the proximity and configuration of the radiation source 40 relative to the container 10; the strength of the bond 32 before radiation weakening; the desired reduction in strength or the desired final strength of the bond 32; and the like. Generally, increasing the exposure of the bond 32 to the radiation decreases the resulting strength of the bond 32. According to one method of the invention, the bond 32 is exposed to the microwave radiation for a duration of at least about 10 minutes, e.g., a duration of about 20 minutes. It will be appreciated that the radiation source 40 alternatively can be configured to emit other types of radiation including, for example, visible and invisible light such as infrared radiation, ultra-violet (UV) radiation, x-rays, or gamma-rays. After weakening, the bond 32 preferably is strong enough to maintain a hermetic seal between the closure 30 and the base portion 12, but weak enough that a person can easily open the container 10.

A grip portion such as a ring, tab, or other feature can also be provided on the closure 30 to facilitate opening. For example, the closure 30 can include a pull ring 34 that is disposed on an outer surface of the closure 30 as shown in FIGS. 1 and 2. Alternatively, the grip portion can be a tab or other feature that can be grasped or otherwise manipulated by a user to open the container 10. The user can grasp the pull ring 34 and urge the pull ring 34 away from the container 10 in a direction 36 to thereby break the bond 32 between the closure 30 and the base portion 12 and peel the closure 30 from the container 10. The closure 30 can be partially or entirely removed from the base portion 12 of the container 10 during opening. Further, the material of the bond 32 can be removed with the closure 30 and/or left attached to the base portion 12 as the closure 30 is removed.

The closure 30 can provide a hermetic seal to the container 10 such that the container 10 can be used for storing food items and other items requiring a hermetic seal and/or a reduced or enhanced storage pressure. Preferably, the bond 32 is sufficiently strong to withstand shear stresses that result from pressures due to the retort process or other processes associated with the manufacture, filling, processing, and/or handling of the container 10; however, a person can easily open the container 10 by subjecting the bond 32 to a tensile force after the bond 32 has been radiation weakened and thereby peeling or otherwise separating the closure 30 from the container 10. For example, the bond 32 can withstand the stresses applied during retort, but tear when put in tension by the user after radiation weakening.

FIG. 3 illustrates the operations for hermetically sealing an open end of a retortable, easy-opening container according to one embodiment of the present invention. It is understood that some of the operations can be omitted and additional operations can be performed without departing from the scope of the present invention. As shown in Block 100, a plastic base portion defining an opening is provided. The base portion can be formed by fusion welding an end ring to a body member such as a cylindrical side of a container. See Block 102. A plastic membrane is disposed to cover the opening. See Block 104. For example, the membrane can be formed by co-extruding a sheet of polypropylene and ethylene vinyl alcohol. Oxygen scavengers can also be provided in polyolefin of the plastic membrane. Further, surfaces of the plastic membrane and/or the container can be primed, e.g., by subjecting the surfaces to a corona. Next, a bond is formed between the membrane and the base portion. See Block 106. The bond can be formed by disposing an adhesive between the plastic membrane and the base portion and urging the plastic membrane and the base portion together. See Block 108. Further, the bond can be formed to have a shear force strength of at least about 20 psi. See Block 110. The container can be retorted or otherwise processed. See Block 112. The bond is then irradiated and thereby weakened so that the bond allows easy opening of the container, i.e., by peeling or otherwise pulling the membrane from the base portion. See Block 114. For example, the bond can be weakened to have a tensile force strength that is less than about 14 pounds. See Block 116. According to one embodiment of the invention, the bond is weakened by irradiating the bond with microwave radiation. See Block 118.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. An easy-opening, retortable container comprising: a base portion having a bottom and side defining an interior space and an opening thereto; and a plastic membrane of sufficient size to cover the opening and having an outer peripheral area attached to the base portion by a radiation weakened bond having a predetermined tensile force strength; and wherein the predetermined tensile force strength of the weakened bond allows easy-opening of the container by peeling the membrane from the base portion.
 2. An easy-opening, retortable container according to claim 1 wherein the base portion is formed of plastic.
 3. An easy-opening, retortable container according to claim 1 wherein the base portion includes a plastic end ring fusion bonded to a body member, the end ring having an outer peripheral area adapted to be joined to the side of the base portion and defining the opening, the plastic membrane being attached to the end ring by the bond.
 4. An easy-opening, retortable container according to claim 1 wherein the predetermined tensile force strength is less than about 14 pounds.
 5. An easy-opening, retortable container according to claim 1 wherein the membrane and the base portion are formed of a high barrier material to prevent transmission of moisture and oxygen therethrough.
 6. An easy-opening, retortable container according to claim 1 wherein the membrane is formed of a co-extruded sheet of polypropylene and ethylene vinyl alcohol.
 7. An easy-opening, retortable container according to claim 1 wherein the membrane includes oxygen scavengers disposed in polyolefin.
 8. An easy-opening, retortable container according to claim 1 wherein the bond is formed of an adhesive.
 9. An easy-opening, retortable container according to claim 8 wherein the adhesive is formed of polyurethane.
 10. An easy-opening, retortable container according to claim 1 wherein the bond is weakened by microwave radiation.
 11. An easy-opening, retortable container comprising: a base portion having a bottom and side defining an interior space and an opening thereto; and a plastic membrane of sufficient size to cover the opening and having an outer peripheral area attached to the base portion by a bond having a predetermined shear force strength and configured to be radiation weakened to have a predetermined tensile force strength; and wherein the predetermined shear force strength of the bond is sufficient to withstand forces created during retort processing of the container, and the predetermined tensile force strength of the bond allows easy-opening of the container by peeling the membrane from the base portion.
 12. An easy-opening, retortable container according to claim 11 wherein the base portion is formed of plastic.
 13. An easy-opening, retortable container according to claim 11 wherein the base portion includes a plastic end ring fusion bonded to a body member, the end ring having an outer peripheral area adapted to be joined to the side of the base portion and defining the opening, the plastic membrane being attached to the end ring by the bond.
 14. An easy-opening, retortable container according to claim 11 wherein the predetermined shear force strength is at least about 20 psi, and the predetermined tensile force strength is less than about 14 pounds.
 15. An easy-opening, retortable container according to claim 11 wherein the membrane and the base portion are formed of a high barrier material to prevent transmission of moisture and oxygen therethrough.
 16. An easy-opening, retortable container according to claim 11 wherein the membrane is formed of a co-extruded sheet of polypropylene and ethylene vinyl alcohol.
 17. An easy-opening, retortable container according to claim 11 wherein the membrane includes oxygen scavengers disposed in polyolefin.
 18. An easy-opening, retortable container according to claim 11 wherein the bond is formed of an adhesive.
 19. An easy-opening, retortable container according to claim 18 wherein the adhesive is formed of polyurethane.
 20. An easy-opening, retortable container according to claim 11 wherein the bond is adapted to be weakened by microwave radiation.
 21. An easy-opening closure for hermetic sealing of an open end of a retortable container, the closure comprising: a plastic end ring having an outside peripheral area adapted to be joined to the open end of the retortable container and an intermediate area extending radially inward from the outer peripheral area and defining an opening to allow access therethrough to the interior of the container; and a plastic membrane of sufficient size to cover the opening and having an outer peripheral area overlapping and attached to the intermediate area of the end ring by a bond having a predetermined shear force strength and configured to be radiation weakened to have a predetermined tensile force strength; and wherein the predetermined shear force strength of the bond is sufficient to withstand forces created during retort processing of the container, and the predetermined tensile force strength of the bond allows easy-opening of the container by peeling the membrane from the end ring.
 22. An easy-opening closure according to claim 21 wherein the plastic end ring is configured to be fusion welded to the container.
 23. An easy-opening closure according to claim 21 wherein the end ring is formed of plastic.
 24. An easy-opening closure according to claim 21 wherein the predetermined shear force strength is at least about 20 psi, and the predetermined tensile force strength is less than about 14 pounds.
 25. An easy-opening closure according to claim 21 wherein the membrane is formed of a high barrier material to prevent transmission of moisture and oxygen therethrough.
 26. An easy-opening closure according to claim 21 wherein the membrane is formed of a co-extruded sheet of polypropylene and ethylene vinyl alcohol.
 27. An easy-opening closure according to claim 21 wherein the membrane includes oxygen scavengers disposed in polyolefin.
 28. An easy-opening closure according to claim 21 wherein the bond is formed of an adhesive disposed between the plastic end ring and the plastic membrane.
 29. An easy-opening closure according to claim 28 wherein the bond is formed of polyurethane.
 30. An easy-opening closure according to claim 21 wherein the bond is adapted to be weakened by microwave radiation.
 31. A method of hermetically sealing an open end of a retortable, easy-opening container, the method comprising: providing a plastic base portion defining an opening; disposing a plastic membrane to cover the opening of the base portion; forming a bond between the membrane and the base portion; and weakening the bond by irradiating the bond such that the bond allows easy opening of the container by peeling the membrane from the base portion.
 32. A method according to claim 31 wherein said providing step comprises fusion welding an end ring to a body member to form the base portion of the container.
 33. A method according to claim 31 wherein said weakening step comprises irradiating the bond with microwave radiation.
 34. A method according to claim 33 wherein said weakening step comprises irradiating the bond with microwave radiation for at least about 10 minutes.
 35. A method according to claim 31 wherein said forming step comprises forming the bond such that the bond has a shear force strength of at least about 20 psi and wherein said weakening step comprises weakening the bond such that the bond has a tensile force strength of less than about 14 pounds.
 36. A method according to claim 31 further comprising co-extruding a sheet of polypropylene and ethylene vinyl alcohol to form the plastic membrane.
 37. A method according to claim 31 further comprising disposing oxygen scavengers in polyolefin to form the plastic membrane.
 38. A method according to claim 31 wherein said forming step comprises disposing an adhesive between the plastic membrane and the base portion and urging the plastic membrane and the base portion together.
 39. A method according to claim 31 further comprising retorting the container after said forming step and prior to said weakening step. 